Modern power applications require a variety of power and current profiles. A motor that operates an elevator is one example. Modern elevator motors usually consist of three-phase motors. These motors often require varying power and current profiles in order to support the heavy duty applications of elevators. The electric drives that deliver power to these motors need to be able to support the power and current requirements.
When a three-phase motor, such as an elevator motor for example, needs a large duty drive, one option is to use two or more smaller drives in parallel to support the duty. The present invention relates to placing two or more drives, of varying power and current profiles, in parallel.
When placing two or more drive in parallel, circulating currents can affect the efficiency of the drive and make for an unequal sharing of current. Additionally, placing two or more drives in parallel may result in a reduction of voltage thereby limiting the operable range of a load device. For example, the motor will have a limited speed range when connected to such a parallel drive.
Therefore, there is a need for a system for placing in two or more drives in parallel that can limit circulating currents between drives, makes current sharing equal between drives, and does not reduce voltage at the system output.